As an important unit of a gas chromatograph system, an inlet is used typically for introducing liquid samples to be analyzed into the gas chromatograph system for vaporization. The vaporized samples are then pushed into a column for analysis. FIG. 1 illustrates the structure of a conventional inlet 1 of a gas chromatograph (GC) system. As can be seen from FIG. 1, the inlet 1 includes a top assembly 7, a shell unit 8, and a liner 9. The liner 9 is typically made of quartz, which can be damaged if not handled properly. Two tubes 70 and 70′ are connected to the top assembly 7 for carrier gas flow and purge gas flow, respectively. The liner 9 is used for vaporizing the sample to be analyzed and is placed inside the shell unit 8. The top portion 90 of the liner 9 is covered by the top assembly 7. Threads 80 are provided on the outer surface of the top portion of the shell unit 8 for engaging with the threads (not shown) on the bottom portion of the top assembly 7. This allows the top assembly 7 to be tightly fastened to compress a sealing rubber O-ring 81 on the liner 9 so as to achieve the effect of preventing the carrier gas and the vaporized sample from leaking out of the system.
Because the samples typically cannot be vaporized completely or be cleaned completely by the carrier gas during operation of the GC system, residue of the samples may remain in the liner 9. This means that the liner 9 needs to be replaced periodically for the sake of accuracy. During replacement, it is necessary to loosen the top assembly 7 from the shell unit 8 first so as to remove the used liner 9. The top assembly 7 is then fastened to the shell unit 8 again once a new liner 9 is placed therein.
Disadvantages are associated with this prior art inlet structure. Firstly, since the sample needs to be vaporized, all parts of the inlet need to be maintained at relatively very high temperatures. Therefore, the user or operator of the GC system will have to get in contact with those high temperature components physically during the replacement operation of the liner. Secondly, the tubes connected to the top assembly restrict the movement of the top assembly and make the thread engagement of the top assembly with the shell unit very difficult. However, if the threads are not engaged correctly and are forced to mate, not only the threads will be damaged, but also the top portion of the liner will be crashed and broken due to the uneven thread engagement.
Because of the above-mentioned disadvantages, there is a need for an improved inlet structure so as to make the replacement operation both simple and user-friendly, and to minimize the possibility of damaging the inlet during the replacement operation of the liner.